1. Field of the Invention
The present invention relates to energy systems as used on drilling rigs. More particularly, the present invention relates to systems for the peak-shaving of the power requirements for drilling rigs. Additionally, and furthermore, the present invention relates to peak-shaving systems as used so as to supply access power during tripping out loads.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
In the field of oil well drilling, significant amount of power is required during the drilling activity. The power requirements as used on a drilling rig serve to supply the drawworks, the mud pumps, the top drives, the rotary tables, the dynamic braking systems and other peripheral loads. In oil well drilling activities, oversized power systems are often utilized so as to meet the “peak” power requirements.
Historically, the number of engines/generators that are used and are typically “online” are more than the required load of the application due to the redundancy and necessary peak KW and VAR demand during certain aspects of the operation. In particular, these peak demands are during the “tripping” of the pipe or drill stem.
During normal operations, there is a base load of lighting, pumps, agitators, mixers, air compressors, etc. This base load can make up typical loads of 400-600 kilowatts. The mud pumps, top drives and rotary tables contribute another fairly consistent KW demand. This demand will vary based on the particular well, depth of drilling, and material being drilled.
During oil well drilling activities, the most intermittent load is the drawworks. This intermittent load is directed toward the peak demand during the raising or lowering of the drill pipe upwardly and downwardly in the well. This peak demand can have loads as much as 2-3 times the base loads of the other demands on the drilling rig.
When drilling and at times when the downhole tool has to be inspected or changed, it is required to pull all of the drill pipe from the hole. This distance can be 10,000 feet or more. The drill pipe must be taken apart and stacked as it is being removed. After repair or replacement, the reverse procedure must take place so as to reinsert all the components back to the desired depth. During the tripping in or out of the hole, the driller (operator) demands extreme power consumption and very quick bursts as the driller raises (or lowers) the string of drill pipe. Since there is a limitation on the height of the drilling mast, the operator must lift the sections in increments and unscrew the different sections. These sections are stacked one at a time. This process is repeated during the reinsertion of the drill pipe back into the hole. This process is referred to as “making a trip”. The intermittent high demand occurs when this load (300,000 pounds or more) occurs over and over again. The load is inconsistent since the weight of the drill stem becomes less and less as sections are removed. The base load requirements for the drilling rig are approximately 600-800 KW. The peak demand can be 1.5 MW and as high as 2.0 MM. Because of these power requirements, the emissions of the engines/generators for a typical land rig are quite high. Newer engines can have much lower MOX output than earlier engines. There are also large amounts of carbon dioxide emissions. The fuel consumption during these intermittent demands can be quite significant.
FIG. 1 illustrates a schematic of the typical drilling rig topology utilizing a common DC bus system. As can be seen in FIG. 1, the AC synchronous engines/generators 10, 12 and 14 are synchronized to an AC bus 16. The AC bus 16 is synchronized onto a common AC fixed frequency/fixed voltage system from which peripheral loads, such as hotel loads, are supplied. The engine/generator 10 is connected to a voltage regulator 18 and to a governor 20. A potential transformer 22 is positioned between the voltage regulator 18 and the engine/generator 10. A cross current line 22 will extend from voltage regulator 18 to the engine/generator 12. A load sharing line 24 is connected to the governor of the various engine/generators. A circuit breaker 26 is positioned between the engine/generator 10 and the common AC bus 16.
The engine/generator 12 and the engine/generator 14 also include respective voltage regulators 28 and 30 and governors 32 and 34. Engine/generators 12 and 14 also have respective circuit breakers 36 and 38. Lines 40, 42 and 44 connect the engine/generators 10, 12 and 14 to the AC bus 16.
Motor control centers 46 and 48 have power transformers 50 and 52 respectively connected along lines 54 and 56 to the AC bus 16. Rectifiers 58 and 60 are placed respective lines 62 and 64 so as to convert the AC power along bus 16 into DC power. Lines 62 and 64 are, in turn, connected to the common DC bus 66.
The common DC bus feeds multiple (or current) source invertors for each of the rig functions. Line 68 is connected to a drawworks motor 70. Line 72 is connected to another drawworks motor 74. Line 76 is connected to a first mud pump motor 78. Line 80 is connected to a second mud pump motor 82. Line 84 is connected to a top drive 86. Line 88 is connected to the rotary table 90. Another line 92 is serves to connect the DC bus to a dynamic braking system 94. Each of the lines 68, 72, 76, 80, 84, 88 and 92 have a respective DC-to-AC variable frequency/variable voltage converters 96, 98, 100, 102, 104, 106, and 108. Each of the lines 68, 72, 76, 80, 84, 88 and 92 also has respective switches 110, 112, 114, 116, 118, 120 and 122 connected thereto. The switches are DC disconnect switches.
As can be seen in FIG. 1, the power requirements of the various motors 70, 74, 78, 82, 86, 90, and 94 must be supplied by the engine/generators 10, 12 and 14. In view of the “peak” requirements of the drawworks motors 70 and 74, the engine/generators 10, 12 and 14 will need to be oversized so as to meet the power requirements. In other circumstances, additional engine/generators must be connected to the AC bus 16 in order to supply the requisite power to the various motors associated with the drilling rig.
It is an object of the present invention to provide an energy storage system which reduces the number of diesel engine/generators required for the power requirements of the drilling rig.
It is an object of the present invention to provide an energy storage system that reduces fuel consumption by the engines/generators of the drilling rig.
It is a further object of the present invention to provide an energy storage system that reduces carbon dioxide and other emissions.
It is still a further object of the present invention to provide an energy storage system which minimizes the requirement for battery replacement.
It is a further object of the present invention to provide an energy storage system that utilizes rechargeable energy storage in order to supplement the power produced from the diesel engine/generators.
It is still a further object of the present invention to provide an energy storage system which creates a redundancy of the DC stored energy that is tied to the DC link with a passive device so as to improve the safety of the system.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.